Plasma processing apparatus

ABSTRACT

A plasma processing apparatus includes an antenna configured to generate plasma of a processing gas in a chamber. The antenna includes: an inner coil provided around the gas supply unit to surround a gas supply unit; and an outer coil provided around the gas supply unit and the inner coil to surround them. The outer coil is configured such that both ends of a wire forming the outer coil are opened; power is supplied from a power supply unit to a central point of the wire; the vicinity of the central point of the wire is grounded; and the outer coil resonates at a wavelength that is a half of a wavelength of the high frequency power. The inner coil is configured such that both ends of a wire forming the inner coil are connected through a capacitor and the inner coil is inductively coupled with the inner coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2017-188480 filed on Sep. 28, 2017, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to a plasma processing apparatus.

BACKGROUND OF THE INVENTION

As for a processing apparatus for performing one of semiconductormanufacturing processes, there is known a plasma processing apparatusfor performing etching, film formation, or the like by converting aprocessing gas into plasma. For example, in a single wafer processingtype plasma processing apparatus, it is required to appropriatelycontrol plasma density distribution in a plane direction of a substratedepending on types of processing. Specifically, the plasma densitydistribution may be controlled based on a structure in the processingchamber or to deal with non-uniform processing in the substrate surfacein post-processing. Therefore, instead of making the plasma densitydistribution uniform over the entire surface of the substrate, theplasma density distribution in a central portion of the substrate may beintentionally made to be different from that in a peripheral portion ofthe substrate.

As for a method of generating plasma in the plasma processing apparatus,there is known a method of exciting a processing gas by supplying a highfrequency power to, e.g., an antenna, and generating an induced electricfield in a processing chamber (see, e.g., Japanese Patent ApplicationPublication No. 2010-258324). In this method, there is disclosed aconfiguration in which a coil-shaped inner antenna and a coil-shapedouter antenna are concentrically provided as an antenna for outputting ahigh frequency, and each antenna resonates at a frequency having awavelength that is a half of that of the high frequency power. Inaccordance with this plasma processing apparatus, it is possible tofinely control in-plane distribution of the plasma density by separatelycontrolling the high frequency power supplied to each antenna.

Further, in an IPC (Inductively Coupled Plasma) type plasma processingapparatus, there is known a technique of supplying a processing gassupplied into a chamber from a center of a dielectric window providedwith an antenna (see, e.g., Japanese Patent Application Publication No.2005-507159).

In the technique disclosed in Japanese Patent Application PublicationNo. 2010-258324, the inner antenna is provided in a circular regionhaving a radius shorter than that of the outer antenna, and thus cannotbe excessively long. Further, in the technique disclosed in JapanesePatent Application Publication No. 2010-258324, each antenna isconfigured to resonate at a frequency having a wavelength that is a halfof that of the supplied high frequency power. Therefore, depending onthe size of the plasma processing apparatus, the frequency of the highfrequency power supplied to the inner antenna should be higher than thefrequency of the high frequency power supplied to the outer antenna.When the frequency of the high frequency supplied to the antenna isincreased, the high frequency power emitted from the antenna tends to beincreased.

Further, in the technique described in Japanese Patent ApplicationPublication No. 2010-258324, it is considered to supply the processinggas into the chamber from the center of the dielectric window providedwith the antenna as described in Japanese Patent Application PublicationNo. 2005-507159. In that case, the inner antenna is disposed near a gasline through which the processing gas is supplied. The high frequency isradiated from the inner antenna. Therefore, abnormal discharge may occurin the gas line provided at the center of the dielectric window. Ifabnormal discharge occurs, the inside of the gas line is damaged, andthe gas line deteriorates. If the inside of the gas line is damaged, amaterial peeled off from the inside of the gas line by the abnormaldischarge scatters as particles in the chamber and may be adhered to thetarget substrate.

SUMMARY OF THE INVENTION

In accordance with an aspect, there is provided a plasma processingapparatus including: a chamber configured to accommodate a targetsubstrate; a dielectric window forming an upper portion of the chamber;a gas supply unit configured to supply a processing gas from an upperportion of the chamber into the chamber; an antenna provided above thechamber to surround the gas supply unit and configured to generateplasma of the processing gas in the chamber by supplying a highfrequency power into the chamber; and a power supply unit configured tosupply a high frequency power to the antenna. The antenna includes: aninner coil provided around the gas supply unit to surround the gassupply unit; and an outer coil provided around the gas supply unit andthe inner coil to surround the gas supply unit and the inner coil. Oneof the inner coil and the outer coil is configured such that both endsof a wire forming the one coil are opened; power is supplied from thepower supply unit to a central point of the wire or a vicinity of thecentral point of the wire; the vicinity of the central point of the wireis grounded; and the one coil resonates at a wavelength that is a halfof a wavelength of the high frequency power supplied from the powersupply unit, and the other one of the inner coil and the outer coil isconfigured such that both ends of a wire forming the other coil areconnected through a capacitor and the other coil is inductively coupledwith the one coil.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present disclosure will become apparentfrom the following description of embodiments, given in conjunction withthe accompanying drawings, in which:

FIG. 1 is a schematic cross sectional view showing an example of aplasma processing apparatus;

FIG. 2 is a schematic perspective view showing an example of an antenna;

FIG. 3 shows an example of arrangement of an inner coil and an outercoil;

FIG. 4 shows an example of changes in a current flowing through theinner coil and a current flowing through the outer coil in the case ofvarying a capacitance of a capacitor of the inner coil;

FIGS. 5A and 5B show examples of a direction of the current flowingthrough the inner coil and a direction of the current flowing throughthe outer coil;

FIG. 6 shows an example of ion current distribution on a wafer;

FIG. 7 is a cross sectional view showing an example of a structure of agas injecting unit in a first embodiment;

FIGS. 8A to 8C show examples of test results obtained by examiningwhether or not discharge has occurred in a comparative example;

FIGS. 9A to 9C show examples of test results obtained by examiningwhether or not discharge has occurred in the first embodiment;

FIGS. 10A and 10B show examples of simulation results of flow of gasinjected from the gas injection unit;

FIGS. 11A and 11B show examples of mass content distribution of reactionby-products on the wafer;

FIGS. 12A to 12C show examples of changes in deposition ratedistribution of a reaction by-product with respect to a gas flow rate inthe case of generating plasma of an etching gas and etching the wafer ina chamber;

FIG. 13 shows another example of the structure of the gas injectionunit;

FIG. 14 shows an example of a structure of a gas injection unit in asecond embodiment;

FIG. 15 shows an example of arrangement of rod-shaped shielding members;

FIG. 16 shows an example of an electric field reduction rate in the gasinjection unit by the shielding members;

FIGS. 17A to 17C show examples of test results obtained by examiningwhether or not discharge has occurred in the second embodiment;

FIG. 18 shows another example of the arrangement of the shieldingmember;

FIG. 19 shows still another example of the arrangement of the shieldingmember;

FIG. 20 shows an example of a structure of a gas injection unit in athird embodiment;

FIGS. 21A to 21C show an example of a test result obtained by examiningwhether or not discharge has occurred in the third embodiment; and

FIG. 22 shows another example of a structure of a gas flow path.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In accordance with one embodiment, there is provided a plasma processingapparatus including: a chamber configured to accommodate a targetsubstrate; a dielectric window forming an upper portion of the chamber;a gas supply unit configured to supply a processing gas from an upperportion of the chamber into the chamber; an antenna provided above thechamber to surround the gas supply unit and configured to generateplasma of the processing gas in the chamber by supplying a highfrequency power into the chamber; and a power supply unit configured tosupply a high frequency power to the antenna. The antenna includes: aninner coil provided around the gas supply unit to surround the gassupply unit; and an outer coil provided around the gas supply unit andthe inner coil to surround the gas supply unit and the inner coil. Oneof the inner coil and the outer coil is configured such that both endsof a wire forming the one coil are opened; power is supplied from thepower supply unit to a central point of the wire or a vicinity of thecentral point of the wire; the vicinity of the central point of the wireis grounded; and the one coil resonates at a wavelength that is a halfof a wavelength of the high frequency power supplied from the powersupply unit, and the other one of the inner coil and the outer coil isconfigured such that both ends of a wire forming the other coil areconnected through a capacitor and the other coil is inductively coupledwith the one coil.

The one coil may be wound two or more turns in a substantially circularspiral shape, the other coil may be formed in a substantially circularring shape, and the one coil and the other coil may be arranged suchthat an outer shape of the one coil and an outer shape of the other coilform concentric circles.

The gas supply unit may have a substantially cylindrical shape, and theone coil and the other coil are arranged such that a center of the outershape of the one coil and a center of the outer shape of the other coilare positioned on a central axis of the gas supply unit.

The one coil and the other coil may be arranged inside the dielectricwindow or above the dielectric window, and a distance between a planeincluding the one coil and a lower surface of the dielectric window maybe different from a distance between a plane including the other coiland the lower surface of the dielectric window.

The one coil may be the outer coil, the other coil may be the innercoil, and the distance between the plane including the inner coil andthe lower surface of the dielectric window may be shorter than thedistance between the plane including the outer coil and the lowersurface of the dielectric window.

The power supply unit may allow a frequency of the high frequency powersupplied to the antenna to be variable.

The capacitor provided at the other coil may be a variable capacitancecapacitor.

A flow path through which the processing gas supplied to the chamberflows may be formed in the gas supply unit, and a pressure in the flowpath may be higher than a pressure in the chamber.

The gas supply unit may include: a protruding part that is a lower partof the gas supply unit and protrudes into the chamber from the lowersurface of the dielectric window; a first injection port provided at theprotruding part and configured to inject the processing gas in adownward direction, and a second injection port provided at theprotruding part and configured to inject the processing gas in ahorizontal direction or in an obliquely downward direction.

A conductive shielding member may be provided at the gas supply unit tosurround a space through which the processing gas passes.

A lower end of the shielding member may be positioned below the lowersurface of the dielectric window.

The shielding member may be formed in a plate shape.

The shielding member may be a metal film formed on an outer wall of thegas supply unit or a sidewall of a space in the gas supply unit throughwhich the processing gas flows.

The shielding member may be formed in a rod shape.

At least a part of the space in the gas supply unit through which theprocessing gas flows may be bent to prevent formation of a linear pathextending from the first injection port and the second injection port toan upper end of the gas supply unit.

In accordance with one embodiment, there is provided a plasma processingapparatus including: a chamber configured to accommodate a targetsubstrate; a dielectric window forming an upper portion of the chamber;a gas supply unit configured to supply a processing gas into the chamberfrom an upper portion of the chamber; an antenna provided above thechamber to surround the gas supply unit and configured to generateplasma of the processing gas in the chamber by supplying a highfrequency power into the chamber; and a power supply unit configured tosupply a high frequency power to the antenna. The antenna is providedaround the gas supply unit to surround the gas supply unit; both ends ofa wire forming the antenna are opened; power is supplied from the powersupply unit to a central point of the wire or to a vicinity of thecentral point of the wire; the vicinity of the central point of the wireis grounded; and the antenna is configured to resonate at a wavelengththat is a half of a wavelength of the high frequency power supplied fromthe power supply unit, and a conductive shielding member is provided atthe gas supply unit to surround a space through which the processing gasflows.

A lower end of the shielding member may be positioned below a lowersurface of the dielectric window.

The shielding member may be formed in a plate shape.

The shielding member may be a metal film formed on an outer wall of thegas supply unit or a sidewall of a space in the gas supply unit throughwhich the processing gas flows.

The shielding member may be formed in a rod shape.

The gas supply unit may include: a protruding part that is a lower partof the gas supply unit and protrudes into the chamber from the lowersurface of the dielectric window; a first injection port provided at theprotruding part and configured to inject the processing gas in adownward direction; and a second injection port provided at theprotruding part and configured to inject the processing gas in ahorizontal direction or in an obliquely downward direction, wherein atleast a part of the space in the gas supply unit through which theprocessing gas flows is bent to prevent formation of a linear pathextending from the first injection port and the second injection port tothe upper end of the gas supply unit.

Hereinafter, embodiments will be described in detail with reference tothe accompanying drawings. The plasma processing apparatus of thepresent disclosure is not limited by the following embodiments. Therespective embodiments can be appropriately combined with each otherwithin a range in which processing contents do not contradict eachother.

First Embodiment

(Configuration of Plasma Processing Apparatus 10)

FIG. 1 is a schematic cross sectional view showing an example of aplasma processing apparatus 10. The plasma processing apparatus 10includes a chamber 11 made of a conductor such as aluminum or the like.An opening 110 for loading/unloading a wafer W that is an example of atarget substrate is provided at a side surface of the chamber 11. Theopening 110 can be opened and closed by a gate valve 111. The chamber 11is grounded.

A disc-shaped susceptor 21 that is made of a conductive material such asaluminum or the like and configured to mount thereon a wafer W as aprocessing target is provided substantially at a center of a bottomsurface of the chamber 11. The susceptor 21 also serves as an electrodefor attracting ions in the plasma (for bias). The susceptor 21 issupported by a cylindrical susceptor support 22 made of an insulator. Inthe present embodiment, a central axis of the susceptor 21 supported bythe susceptor support 22 is defined as the Z-axis.

A high frequency bias power supply 30 is connected to the susceptor 21via a power feed rod 32 and a matching circuit 31. A high frequencypower having a frequency of, e.g., 13 MHz, is supplied from the highfrequency power supply 30 to the susceptor 21. The frequency and thepower of the high frequency power supplied from the high frequency powersupply 30 to the susceptor 21 are controlled by a control device 100 tobe described later.

An electrostatic chuck 23 for holding the wafer W by an electrostaticattraction force is provided on an upper surface of the susceptor 21. Afocus ring 24 is provided on an outer circumferential side of theelectrostatic chuck 23 to surround a periphery of the wafer W. Thesubstantially disc-shaped wafer W is mounted on the electrostatic chuck23 such that the central axis thereof coincides with the Z-axis.

A flow path 212 through which a coolant such as cooling water (C.W.) orthe like flows to control a temperature of the wafer W is formed insidethe susceptor 21. The flow path 212 is connected to a chiller unit (notshown) through a line 213, and the coolant having a controlledtemperature is supplied from the chiller unit to the flow path 212through the line 213. The temperature of the coolant in the chiller unitis controlled by the control device 100 to be described later.

Inside the susceptor 21, a gas supply line 214 for supplying a heattransfer gas, e.g., He gas or the like, is provided between an uppersurface of the electrostatic chuck 23 and a backside of the wafer W. Thegas supply line 214 penetrates through the electrostatic chuck 23. Anupper end of the gas supply line 214 is opened on the upper surface ofthe electrostatic chuck 23.

The susceptor 21 is provided with lifting pins that penetrate throughthe susceptor 21 in a vertical direction and are configured to protrudebeyond and retract below the upper surface of the electrostatic chuck 23to transfer the wafer W with respect to a transfer arm (not shown). Thevertical movement of the lift pins is controlled by the control device100 to be described later.

An annular baffle plate 12 having a plurality of through-holes isprovided between an outer wall of the susceptor support 22 and an innerwall of the chamber 11. A gas exhaust port 13 is formed on the bottomsurface of the chamber 11, and connected to a gas exhaust unit 15through a gas exhaust line 14. The gas exhaust unit 15 is controlled bythe control device 100 to be described later.

A disc-shaped dielectric window 53 made of a dielectric material, e.g.,quartz or the like, is provided at an upper portion of the chamber 11. Aspace above the dielectric window 53 is covered with a cylindricalshield box 51 made of a conductor, e.g., aluminum or the like. Theshield box 51 is grounded via the chamber 11. An opening is provided atthe center of the shield box 51 and that of the dielectric window 53. Agas injection unit 41 for supplying a processing gas into the chamber 11is provided at the opening. The gas injection unit 41 has asubstantially cylindrical outer shape. Further, the gas injection unit41 is provided at the central openings of the shield box 51 and thedielectric window 53 such that the central axis of the gas injectionunit 41 coincides with the Z-axis. The gas injection unit 41 is anexample of a gas supply unit.

Inlet ports 42 a and 42 b for introducing a processing gas into the gasinjection unit 41 are provided at an upper portion of the gas injectionunit 41. A lower portion of the gas injection unit 41 protrudes downwardfrom a lower surface of the dielectric window 53. Formed at the lowerportion of the gas injection unit 41 are injection ports 43 a forinjecting the processing gas in a downward direction along the Z-axisand injection ports 43 b for injecting the processing gas in ahorizontal direction, i.e., in a direction away from the Z-axis. Theinjection port 43 a is an example of a first injection port. Theinjection port 43 b is an example of a second injection port.

A gas supply source 44 a is connected to the inlet port 42 a via a valve46 a and an MFC (Mass Flow Controller) 45 a. A gas supply source 44 b isconnected to the inlet port 42 b via a valve 46 b and an MFC 45 b.

The MFC 45 a controls a flow rate of the processing gas supplied fromthe gas supply source 44 a. The valve 46 a controls supply of theprocessing gas at a flow rate is controlled by the MFC 45 a to the gasinjection unit 41 and stop of the supply. The processing gas introducedinto the gas injection unit 41 through the inlet port 42 a is injectedin a downward direction into the chamber 11 through the injection ports43 a.

The MFC 45 b controls a flow rate of the processing gas supplied fromthe gas supply source 44 b. The valve 46 b controls supply of theprocessing gas at a flow rate controlled by the MFC 45 b to the gasinjection unit 41 and stop of the supply. The processing gas introducedinto the gas injection unit 41 through the inlet port 42 b is injectedinto the chamber 11 through the injection ports 43 b in a horizontaldirection. The MFCs 45 a and 45 b, and the valves 46 a and 46 b areindependently controlled by the control device 100 to be describedlater.

In the present embodiment, an etching gas, e.g., CF₄ gas, chlorine gas,or the like, is supplied as the processing gas from the gas supplysources 44 a and 44 b into the chamber 11. Different processing gasesmay be supplied from the gas supply sources 44 a and 44 b into thechamber 11, respectively.

An antenna 54 for plasma generation is accommodated in a space that issurrounded by the dielectric window 53 and the shield box 51 at aposition above the chamber 11. The antenna 54 includes an outer coil 541and an inner coil 542. The inner coil 542 is provided around the gasinjection unit 41 to surround the gas injection unit 41. The outer coil541 is provided around the gas injection unit 41 and the inner coil 542to surround the gas injection unit 41 and the inner coil 542. The outercoil 541 and the inner coil 542 are supported by a support mechanism(not shown) to be positioned above the dielectric window 53 while beingseparated from the dielectric window 53. Further, the outer coil 541 andthe inner coil 542 are not necessarily separated from the dielectricwindow 53. One or both of the outer coil 541 and the inner coil 542 maybe in contact with an upper surface of the dielectric window 53.Further, one or both of the outer coil 541 and the inner coil 542 may beformed inside the dielectric window 53.

(Structure of the Antenna 54)

FIG. 2 is a schematic perspective view showing an example of the antenna54. As shown in FIG. 2, for example, the outer coil 541 is wound two ormore turns in a substantially circular spiral shape. The outer coil 541is provided above the dielectric window 53 such that the central axis ofthe outer shape of the outer coil 541 coincides with the Z-axis. Asshown in FIG. 2, for example, the inner coil 542 is formed in asubstantially circular ring shape and is provided above the dielectricwindow 53 such that the center axis of the inner coil 542 coincides withthe Z-axis.

In the present embodiment, the outer coil 541 and the inner coil 542 areplanar coils and arranged above the lower surface of the dielectricwindow 53 to be substantially in parallel to the surface of the wafer Wmounted on the electrostatic chuck 23, the lower surface being aboundary surface with respect to a plasma generation space. Further, inthe present embodiment, a distance between the outer coil 541 and thelower surface of the dielectric window 53 is different from a distancebetween the inner coil 542 and the lower surface of the dielectricwindow 53. For example, the distance between the inner coil 542 and thelower surface of the dielectric window 53 is shorter than the distancebetween the outer coil 541 and the lower surface of the dielectricwindow 53. In another example, the distance between the outer coil 541and the upper surface of the dielectric window 53 and the distancebetween the inner coil 542 and the upper surface of the dielectricwindow 53 may be the same. The distance between the outer coil 541 andthe upper surface of the dielectric window 53 may be longer than thedistance between the inner coil 542 and the upper surface of thedielectric window 53. The distance between the outer coil 541 and thelower surface of the dielectric window 53 and the distance between theinner coil 542 and the lower surface of the dielectric window 53 may beindependently changed by a driving unit (not shown).

FIG. 3 shows an example of arrangement of the inner coil 542 and theouter coil 541. FIG. 3 shows an example of the arrangement of the innercoil 542 and the outer coil 541 when viewed from the Z-axis direction.The inner coil 542 has a circular shape with a radius r3 and is arrangedsuch that the center of the circle coincides with the Z-axis. In thepresent embodiment, the radius r3 is, e.g., 75 mm or less.

The outer coil 541 has a substantially circular spiral shape in a regionbetween a circle having a radius r1 and a circle having a radius r2. Theouter coil 541 is provided such that the center of the circle having theradius r1 and the center of the circle having the radius r2 coincidewith the Z-axis. In other words, the outer coil 541 and the inner coil542 are arranged such that the outer shape of the outer coil 541 and theouter shape of the inner coil 542 form concentric circles. In thepresent embodiment, the radius r1 is, e.g., 140 mm, and the radius r2is, e.g., 210 mm.

Both ends of a wire forming the outer coil 541 are opened. The highfrequency power supply 61 is connected to a central point of the wireforming the outer coil 541 or to a vicinity of the central point, andthe high frequency power is supplied from the high frequency powersupply 61 to the outer coil 541. The high frequency power supply 61 isan example of a power supply unit. Further, the vicinity of the centralpoint of the wire forming the outer coil 541 is grounded. The outer coil541 is configured to resonate at a wavelength that is a half of awavelength λ of the high frequency power supplied from the highfrequency power supply 61. In other words, the outer coil 541 functionsas a planar helical resonator. A voltage generated in the wire formingthe outer coil 541 is distributed such that it becomes minimum near thecentral point of the wire and becomes maximum at both ends of the wire.In addition, a current generated in the wire forming the outer coil 541is distributed such that it becomes maximum near the central point ofthe wire and becomes minimum at both ends of the wire. The frequency andthe power of the high frequency power supplied from the high frequencypower supply 61 to the outer coil 541 can be changed. The frequency andthe power of the high frequency power supplied from the high frequencypower supply 61 to the outer coil 541 are controlled by the controldevice 100 to be described later.

Both ends of a wire forming the inner coil 542 are connected to eachother through a capacitor 543. In the present embodiment, the capacitor543 is a variable capacitor. The capacitor 543 may be a capacitor havinga fixed capacitance. The inner coil 542 is inductively coupled with theouter coil 541. The current flows through the inner coil 542 in adirection to cancel a magnetic field generated by the current flowingthrough the outer coil 541. It is possible to control the direction orthe magnitude of the current flowing through the inner coil 542 withrespect to the current flowing through the outer coil 541 by controllingthe capacitance of the capacitor 543. The capacitance of the capacitor543 is controlled by the control device 100 to be described later.

A magnetic field is generated in the Z-axis direction by the currentflowing through the outer coil 541 and the current flowing through theinner coil 542, and an induced electric field is generated in thechamber 11 by the generated magnetic field. Due to the induced electricfield generated in the chamber 11, the processing gas supplied into thechamber 11 from the gas injection unit 41 is converted into plasma.Predetermined processing such as etching or the like is performed on thewafer W on the electrostatic chuck 23 by ions and active speciescontained in the plasma.

Here, it is considered to provide a planar type helical resonator havinga similar size to that of the inner coil 542, instead of the inner coil542, inside the outer coil 541 (the gas injection unit 41 side). Sincethe inner region of the outer coil 541 is smaller than the region wherethe outer coil 541 is disposed, it is difficult to provide a line havingthe same length as that of the wire forming the outer coil 541 in theinner region of the outer coil 541. Therefore, the wire forming theplanar helical resonator (hereinafter, referred to as “inner resonator”)disposed in the inner region of the outer coil 541 should be shorterthan the wire forming the outer coil 541. If the wire becomes shorter,the resonance frequency is increased. Therefore, the resonance frequencyof the inner resonator should be higher than that of the outer coil 541.When the frequency becomes higher, the energy of the electromagneticwave radiated from the coil becomes higher.

The gas injection unit 41 is arranged in the inner resonator. The innerresonator and the gas injection unit are close to each other. Therefore,electromagnetic waves radiated from the inner resonator enter the spacein the gas injection unit 41 where the processing gas flows. When theresonance frequency of the inner resonator becomes higher, the energy ofthe electromagnetic waves radiated from the inner resonator becomeshigher. Therefore, electromagnetic waves of higher energy enter thespace in the gas injection unit 41 where the processing gas flows.Accordingly, abnormal discharge may occur in the space in the gasinjection unit 41 where the processing gas flows.

The energy of the electromagnetic waves entering the space in the gasinjection unit 41 from the inner resonator may be suppressed byseparating the inner resonator from the gas injection unit 41. However,when the inner resonator is separated from the Z-axis, it is difficultto independently control the plasma in the region near the Z-axis andthe plasma in the region far from the Z-axis. Therefore, the innerresonator contributing to the control of the plasma near the Z-axisneeds to be located near the gas injection unit 41. Accordingly, in thecase of using the inner resonator, it is difficult to avoid abnormaldischarge occurring in the space in the gas injection unit 41 where theprocessing gas flows.

On the other hand, in the present embodiment, a loop-shaped inner coil542 having both ends connected by a capacitor 543 is provided, insteadof the planar helical resonator, inside the outer coil 541 (the gasinjection unit 41 side). The inner coil 542 generates an induced currentin response to the magnetic field generated by the current flowingthrough the outer coil 541 without resonating by the directly suppliedhigh frequency power. Therefore, the current having the same frequencyas that of the current flowing through the outer coil 541 flows throughthe inner coil 542 regardless of the length of the wire forming theinner coil 542. Accordingly, even when the length of the wire formingthe inner coil 542 is shorter than that of the wire forming the outercoil 541, the current having the same frequency as that of the currentflowing through the outer coil 541 can be generated in the inner coil42.

Since the region where the outer coil 541 is disposed is greater thanthe inner region of the outer coil 541, a relatively long line can beused as the wire forming the outer coil 541 and, thus, the outer coil541 functioning as a planar type helical resonator can resonate at arelatively low frequency. Therefore, a current having a relatively lowfrequency that is the same as the frequency of the current flowingthrough the outer coil 541 is generated in the inner coil 542.Accordingly, the energy of electromagnetic waves radiated from the innercoil 542 is suppressed, and the energy of electromagnetic waves enteringthe gas injection unit 41 is suppressed. As a result, it is possible tosuppress occurrence of abnormal discharge in the space in the gasinjection unit 41.

Referring back to FIG. 1, the explanation will be continued. The plasmaprocessing apparatus 10 includes the control device 100 for controllingthe respective components of the plasma processing apparatus 10. Thecontrol device 100 includes a memory such as a ROM (Read Only Memory), aRAM (Random Access Memory), or the like, and a processor such as a CPU(Central Processing Unit) or the like. Data such as recipes and thelike, programs, and the like are stored in the memory in the controldevice 100. The processor in the control device 100 reads out andexecutes the program stored in the memory inside the control device 100and controls the respective components of the plasma processingapparatus 10 based on the data such as the recipes and the like storedin the memory in the control device 100.

(Current Flowing Through the Outer Coil 541 and Current Flowing Throughthe Inner Coil 542)

FIG. 4 shows an example of changes in the current flowing through theinner coil 542 and the current flowing through the outer coil 541 in thecase of varying the capacitance of the capacitor 543 of the inner coil542. FIG. 4 shows the changes in the current flowing through the innercoil 542 and the current flowing through the outer coil 541 in the caseof varying the range of the capacitance of the capacitor 543 from 10 pFto 100 pF in 0 to 19200 steps by a stepping motor.

The test result shown in FIG. 4 was obtained mainly under the followingconditions.

-   -   Pressure in the chamber 11: 100 mT    -   Processing gas: Ar/CF₄=70/10 sccm    -   High frequency power supplied to the outer coil 541: 1000 W    -   Frequency of the high frequency power supplied to the outer coil        541: 27 MHz

As shown in FIG. 4, for example, as the capacitance of the capacitor 543is increased from 10 pF (capacitance corresponding to 0 step), theenergy supplied from the outer coil 541 to the inner coil 542 byelectromagnetic induction is increased and, thus, the current flowingthrough the inner coil 542 is increased. On the other hand, as theenergy supplied to the inner coil 542 is increased, the energy of theouter coil 541 is decreased and, thus, the current flowing through theouter coil 541 is decreased. When the capacitance of the capacitor 543becomes close to the capacitance corresponding to 12200 steps, thecurrent flowing through the inner coil 542 becomes maximum and thecurrent flowing through the outer coil 541 becomes substantially thesame as that flowing through the inner coil 542.

When the capacitance of the capacitor 543 is further increased from thecapacitance corresponding to 12200 steps to the capacitancecorresponding to 12400 steps, the polarity of the current flowingthrough the inner coil 542 is inverted and a large current flows in theopposite direction. This is because the direction of the current flowingthrough the outer coil 541 and the direction of the current flowingthrough the inner coil 542 are the same (in-phase) at the capacitancefrom 0 step to 12400 steps as can be seen from FIG. 5A, and thedirection of the current flowing through the outer coil 541 and thedirection of the current flowing through the inner coil 542 are opposite(reversed-phase) at the capacitance from 12400 steps to 19200 steps ascan be seen from FIG. 5B, for example.

FIG. 6 shows an example of ion current distribution on the wafer W. Theion current was measured in a radial direction from the central portionof the wafer W toward the outer peripheral portion of the wafer W byusing a planar Langmuir probe. FIG. 6 shows the distribution of the ioncurrent with respect to the capacitance of the capacitor 543corresponding to each step in a state where the ion current at thecentral portion of the wafer W is normalized to 1. The magnitude of theion current on the wafer W is correlated with the density of the plasmaon the wafer W. Therefore, the ion current distribution on the wafer Wcorresponds to the plasma density distribution on the wafer W.

Referring to FIG. 6, in the case of the capacitance of the capacitor 543which corresponds to the 0 step, the ion current is slightly increasedat a position slightly outer than the center of the wafer W. As thecapacitance of the capacitor 543 is increased, the ion current near thecenter of the wafer W becomes relatively greater. This is because thedirection of the current flowing through the outer coil 541 and that ofthe current flowing through the inner coil 542 are the same (same phase)as can be seen from FIG. 5A, for example, and the ion current near thecenter of the wafer W is increased due to the strong induced electricfield generated by the magnetic field generated by both coils.

On the other hand, in the case of the capacitance of the capacitor 543which corresponds to the 12400 steps, the ion current is relativelysmall near the center of the wafer W. This is because the direction ofthe current flowing through the outer coil 541 and that of the currentflowing through the inner coil 542 are opposite (anti-phase), as can beseen from FIG. 5B, for example, and the ion current near the center ofthe wafer W is decreased due to the weak induced electric fieldgenerated by the magnetic field generated by both coils.

By controlling the capacitance of the capacitor 543 connected to theinner coil 542, the plasma density distribution in the radial directionabout the Z-axis on the wafer W can be controlled. Accordingly, theaccuracy of the processing on the wafer W can be improved.

(Structure of the Gas Injection Unit 41)

FIG. 7 is a cross sectional view showing an example of the structure ofthe gas injection unit 41 in the first embodiment. The gas injectionunit 41 is made of a dielectric material, e.g., ceramic, quartz, or thelike, and has a substantially cylindrical outer shape. The gas injectionunit 41 is fitted to the opening formed at the center of the shield box51 and the opening formed at the center of the dielectric window 53 andfixed to the dielectric window 53 by screws 411. The gas injection unitis fixed to the dielectric window 53 such that the central axis thereofcoincides with the Z-axis. A lower part 410 of the gas injection unit 41protrudes more downward than the lower surface of the dielectric window53. The lower part 410 of the gas injection unit 41 is an example of aprotruding part.

A plurality of injection ports 43 a and a plurality of injection ports43 b are formed at the lower part 410 of the gas injection unit 41. Theinjection ports 43 a are formed on the circumference about the Z-axiswhich corresponds to the lower surface of the gas injection unit 41 andinject the processing gas in a downward direction. The injection ports43 b are formed at the sidewall of the lower part 410 of the gasinjection unit 41 and inject the processing gas in the horizontaldirection.

The processing gas supplied through the inlet port 42 a passes through asubstantially cylindrical space 430 a having the Z-axis as the centralaxis thereof and is injected in a downward direction through theinjection ports 43 a. The processing gas supplied through the inlet port42 b passes through a space 430 b provided around the space 430 a and isinjected through the injection ports 43 b radially about the Z-axis. Thespace 430 a and the space 430 b are examples of flow paths through whichthe processing gas supplied to the chamber 11 flows.

A transparent window 421 made of quartz or the like is provided on theupper portion of the gas injection unit 41. The window 421 allowswhether or not discharge has occurred in the space 430 a to be detected.The window 421 also allows the intensity, the wavelength, or the like ofthe light emitted from the plasma in the chamber 11 through the space430 a and the injection ports 43 a to be observed.

(Test Result)

Next, a test was conducted to examine whether or not abnormal dischargehas occurred in the gas injection unit 41 in the case of generatingplasma in the chamber 11. FIGS. 8A to 8C show examples of the testresults obtained by examining whether or not discharge has occurred inthe comparative example. FIG. 8A shows the test result obtained when thepressure in the chamber 11 is 10 mT. FIG. 8B shows the test resultobtained when the pressure in the chamber 11 is 100 mT. FIG. 8C showsthe test result obtained when the pressure in the chamber 11 is 400 mT.In the comparative example, the test was conducted by providing an innerresonator instead of the inner coil 542. In the test, the high frequencypower was not applied to the outer coil 541.

The main conditions of the test in the comparative example are asfollows.

-   -   Pressure in the chamber 11: 10 to 400 mT    -   Processing gas: Ar=100 to 1500 sccm    -   High frequency power supplied to the inner resonator: 100 to 650        W    -   Frequency of the high frequency power supplied to the inner        resonator: 60 MHz

In FIGS. 8A to 8C, the condition in which the abnormal discharge has notoccurred is expressed by ◯, and the condition in which the abnormaldischarge has occurred is expressed by x. As shown in FIGS. 8A to 8C, inthe comparative example in which the inner resonator is used instead ofthe inner coil 542, abnormal discharge has occurred in the gas injectionunit 41 under substantially all conditions. The pressure in the spaces430 a and 430 b of the gas injection unit 41 was considerably higherthan that in the chamber 11. The pressure in the spaces 430 a and 430 bwas within a range from 3 Torr and 25 Torr.

FIGS. 9A to 9C show examples of test results obtained by examiningwhether or not discharge has occurred in the first embodiment. FIG. 9Ashows the test result obtained when the pressure in the chamber 11 is 10mT. FIG. 9B shows the test result obtained when the pressure in thechamber 11 is 100 mT. FIG. 9C shows the test result obtained when thepressure in the chamber 11 is 400 mT.

The test results shown in FIGS. 9A to 9C were obtained mainly under thefollowing conditions.

-   -   Pressure in the chamber 11: 10 to 400 mT    -   Processing gas: Ar=100 to 1500 sccm    -   High frequency power supplied to the outer coil 541: 100 to 2000        W    -   Frequency of the high frequency power supplied to the outer coil        541: 27 MHz

The test was conducted while setting the capacitance of the capacitor543 connected to the inner coil 542 to the capacitance corresponding to12200 steps shown in FIG. 4. As shown in FIG. 9, for example, in thefirst embodiment, abnormal discharge has not occurred in the gasinjection unit 41 under all conditions. The occurrence of abnormaldischarge in the gas injection unit 41 can be suppressed by providingthe inner coil 542 inside the outer coil 541. Further, the plasmadensity distribution on the wafer W can be controlled by controlling thecapacitance of the capacitor 543 of the inner coil 542 as shown in FIG.6.

(Simulation of the Flow of Gas Injected from the Gas Injection Unit 41)

In the present embodiment, as shown in FIG. 7, for example, the lowerpart 410 of the gas injection unit 41 is provided with the injectionports 43 a for injecting gas in a downward direction and the injectionports 43 b for injecting gas in a horizontal direction. FIGS. 10A and10B show examples of the simulation results of the flow of the gasinjected from the gas injection unit 41. FIG. 10A shows the simulationresult of the flow of the gas injected in a downward direction from theinjection ports 43 a. FIG. 10B shows the simulation result of the flowof the gas injected in a horizontal direction from the injection ports43 b.

The main conditions of the simulation are as follows.

-   -   Pressure in chamber 11: 50 mT    -   Processing gas: Ar=500 sccm    -   Reaction by-product: SiCl₄=50 sccm (entire surface of the wafer        W)

The reaction by-product is a substance generated as a result of thereaction between the wafer W and particles generated from the plasma ofthe etching gas at the time of etching the wafer W. In the simulation,it is assumed that the reaction by-product is SiCl₄ that is a compoundof silicon contained in the wafer W and halogen contained in the etchinggas and it is uniformly supplied into the chamber 11 from the entiresurface of the wafer W.

When the gas is injected in a downward direction, strong gas flowdirected from the center of the wafer W toward the edge of the wafer isgenerated near the center of the wafer W as can be seen from FIG. 10A,for example. Accordingly, the generated reaction by-product isefficiently removed near the center of the wafer W. Since, however, thegas flow is weak near the edge of the wafer W, the effect of removingthe reaction by-product is low near the edge of the wafer W.

On the other hand, when gas is injected in a horizontal direction,strong gas flow is generated near the edge of the wafer W, whereas thegas flow near the center of the wafer W is weak, as can be seen fromFIG. 10B, for example. Therefore, the generated reaction by-product isefficiently removed near the edge of the wafer W. However, the effect ofremoving the reaction by-product is low near the center of the wafer W.

FIGS. 11A and 11B show examples of the mass content distribution of thereaction by-product on the wafer W. FIG. 11A shows the mass contentdistribution of the reaction by-product on the wafer W in the case ofsetting the flow rate of Ar gas to 500 sccm. FIG. 11B shows the masscontent distribution of the reaction by-product on the wafer W in thecase of setting the flow rate of Ar gas to 45 sccm.

As clearly can be seen from FIG. 11A, for example, when the gas isinjected in a downward direction from the injection ports 43 a, thecontent ratio of the reaction by-product is lower near the center of thewafer W than near the edge of the wafer W, and the reaction by-productis removed more efficiently near the center of the wafer W than near theedge of the wafer W. On the other hand, when the gas is injected in ahorizontal direction from the injection ports 43 b, the content ratio ofthe reaction by-product is slightly lower near the edge of the wafer Wthan near the center of the wafer W, and the reaction by-product isremoved more efficiently near the edge of the wafer W than near thecenter of the wafer W.

The result of FIG. 11A shows that strong gas flow can be generated nearboth of the center and the edge of the wafer W by combining the downwardgas injection from the injection ports 43 a and the horizontal gasinjection from the injection ports 43 b. Accordingly, the reactionby-product generated on the wafer W can be efficiently removed. When theflow rate of the injected gas is small, the content ratio of thereaction by-product is increased and the reaction by-product removaleffect is decreased regardless of the gas injection direction, as can beseen from FIG. 11B, for example. Therefore, it is required to increasethe flow rate of the gas injected from the injection ports 43 a and 43b.

(Influence on the Processing by the Flow of Gas Injected from the GasInjection Unit 41)

FIGS. 12A to 12C show examples of changes in deposition ratedistribution of the reaction by-product with respect to the gas flowrate in the case of generating plasma of the etching gas and etching thewafer W in the chamber 11. At this time, the wafer W is made of silicon;Cl₂, HBr, Ar and O₂ are used as the etching gas; and the reactionby-product is SiOClBr. The reaction by-product is discharged from thesurface of the wafer W into the chamber 11 by etching. However, a partof the reaction by-product is re-adhered to the wafer W. Therefore, theamount of the reaction by-product re-adhered to the wafer W is measuredas a deposition rate. FIG. 12A shows the deposition ratio distributionof the reaction by-product in the case of injecting the gas in adownward direction. FIG. 12B shows the deposition ratio distribution ofthe reaction by-product in the case of injecting the gas in a horizontaldirection. In FIG. 12C, the deposition rate distribution of the reactionby-product in the case of injecting the gas from the sidewall of thechamber 11 toward the Z-axis is shown as a comparative example. The flowrates shown in FIGS. 12A to 12C indicate the flow rates of the etchinggas. A reference flow rate is 500 sccm.

When the flow rate of the gas injected in a downward direction isincreased, the deposition ratio of the reaction by-product near thecenter of the wafer W is considerably decreased, whereas the depositionratio of the reaction by-product near the edge of the wafer W is hardlychanged, as can be seen from FIG. 12A, for example. On the other hand,when the flow rate of the gas injected in a horizontal direction isincreased, the deposition rate of the reaction by-product near the edgeof the wafer W is considerably decreased, whereas the deposition ratioof the reaction by-product near the center of the wafer W is hardlychanged, as can be seen from FIG. 12B, for example.

Since the deposition rate of reaction by-product is proportional to theremaining amount of reaction by-product therearound, it is consideredthat the reaction by-product can be removed efficiently near both of thecenter and the edge of the wafer W by combining the downward gasinjection from the injection ports 43 a and the horizontal gas injectionfrom the injection ports 43 b, as can be seen from the results of FIGS.12A and 12B.

When the gas is injected from the sidewall of the chamber 11 toward theZ-axis, as the flow rate of the injected gas is decreased, thedeposition rate is higher at a position between the vicinity of thecenter of the wafer W and the vicinity of the edge of the wafer W. Asthe flow rate of the injected gas is increased, the deposition rate inthe vicinity of the edge of the wafer W is decreased and the depositionrate in the vicinity of the center of the wafer W is increased, as canbe seen from FIG. 12C, for example. This is because the gas is injectedfrom the sidewall of the chamber 11 and, thus, the reaction by-productin the vicinity of the edge of the wafer W is pushed toward the vicinityof the center of the wafer W as the flow rate of the gas is increased.Accordingly, when the gas is injected from the sidewall of the chamber11 toward the Z-axis, it is difficult to efficiently remove the reactionby-product on the wafer W.

The first embodiment has been described above. As apparent from theabove description, in accordance with the plasma processing apparatus 10of the present embodiment, it is possible to finely control the plasmadensity distribution while suppressing occurrence of abnormal discharge.Further, in the present embodiment, the processing gas is injected in adownward direction and in a horizontal direction from the gas injectionunit 41 and, thus, the reaction by-product generated on the wafer W canbe removed efficiently.

In the above-described first embodiment, each of the injection ports 43b injects the processing gas in a horizontal direction as shown in FIG.7, for example. However, the present disclosure is not limited thereto.As shown in FIG. 13, for example, each of the injection ports 43 b maybe configured to inject the processing gas in a direction away from theZ-axis, i.e., in an obliquely downward direction. FIG. 13 shows anotherexample of the structure of the gas injection unit 41.

Second Embodiment

In the first embodiment, the occurrence of abnormal discharge in the gasinjection unit 41 was suppressed by providing the inner coil 542 insidethe outer coil 541. On the other hand, in the second embodiment, theoccurrence of abnormal discharge in the gas injection unit 41 issuppressed by providing a shielding member around a space in the gasinjection unit 41 where the processing gas flows.

(Structure of the Gas Injection Unit 41)

FIG. 14 shows an example of the structure of the gas injection unit 41in the second embodiment. Among the components shown in FIG. 14, thecomponents denoted by like reference numerals as those of the componentsshown in FIG. 7 have the same functions as those described withreference to FIG. 7, except for the following features. Therefore,detailed description thereof will be omitted.

In the gas injection unit 41 of the present embodiment, as shown in FIG.14, for example, a plate-shaped shielding member 420 is provided at asidewall forming the space 430 a in the gas injection unit 41. Theshielding member 420 is made of a non-magnetic conductive metal such astitanium or the like. A lower end of the shielding member 420 extendsdownward from the lower surface of the dielectric window 53. Forexample, the shielding member 420 is a metal film formed by thermallyspraying titanium or the like on the sidewall forming the space 430 a inthe gas injection unit 41. Since the space 430 a in the gas injectionunit 41 is substantially cylindrical, the shielding member 420 is formedin a cylindrical shape.

By providing the shielding member 420 at the sidewall forming the space430 a in the gas injection unit 41, the electromagnetic wave generatedfrom the antenna 54 is prevented from entering the space 430 a.Accordingly, the occurrence of abnormal discharge in the space 430 a issuppressed. In the example shown in FIG. 14, the shielding member 420 isprovided at the sidewall forming the space 430. However, the shieldingmember 420 may also be provided at a sidewall of each space 430 b.

In the example shown in FIG. 14, the plate-shaped shielding member 420is provided at the sidewall forming the space 430 a. However, in anotherexample, a plurality of rod-shaped shielding members 420 may be providedaround the space 430 a. FIG. 15 shows an example of the arrangement ofthe rod-shaped shielding members 420. FIG. 15 is a cross sectional viewof the gas injection unit 41 when viewed from the Z-axis direction. Inthe example shown in FIG. 15, eight rod-shaped shielding members 420 areinterposed between adjacent spaces 430 b. However, eight or moreshielding members 420 may be arranged around the space 430 a. When eightor more shielding members 420 are arranged around the space 430 a, theshielding members 420 may be provided in the sidewall outer than thespace 430 b instead of being interposed between the adjacent spaces 430b. Accordingly, the occurrence of abnormal discharge in the space 430 bcan also be suppressed.

FIG. 16 shows examples of an electric field reduction rate of the gasinjection unit 41 by the shielding member 420. FIG. 16 shows the resultsof the simulation on the electric field reduction ratio in the case ofproviding different shielding members 420 with respect to an electricfield intensity applied to a region of the lower part 410 of the gasinjection unit 41 which includes the space 430 a and the space 430 b inthe case of not providing the shielding member 420. Further, in FIG. 16,a high frequency power of 60 MHz and 1 kW is supplied to an innerresonator used instead of the inner coil 542, and the inner resonatorresonates at a wavelength that is a half of that of the high frequencypower. An upper portion, an intermediate portion, and a lower portionshown in FIG. 16 represent an upper portion, an intermediate portion,and a lower portion of the region of the lower part 410 of the gasinjection unit 41, respectively. In FIG. 16, the simulation wasconducted while setting a thickness of the cylindrical shielding member420 (cylindrical shield) shown in FIG. 14, for example, to 0.5 mm, and adiameter of the rod-shaped shielding member 420 (rod-shaped shield)shown in FIG. 15, for example, to 2 mm.

As shown in FIG. 16, for example, in any type of the shield members 420,the electric field intensity applied to the region of the lower part 410of the gas injection unit 41 was reduced and the shielding effect wasrealized. The shielding effect of the cylindrical shield is higher thanthat of the rod-shaped shield. The shielding effect is improved as thenumber of rod-shaped shields is increased, i.e., as a gap between therod-shaped shields is reduced.

FIGS. 17A to 17C show examples of test results obtained by examiningwhether or not discharge has occurred in the second embodiment. FIG. 17Ashows the test result obtained when the pressure in the chamber 11 is 10mT. FIG. 17B shows the test result obtained when the pressure in thechamber 11 is 100 mT. FIG. 17C shows the test result obtained when thepressure in the chamber 11 is 400 mT. In the tests shown in FIGS. 17A to17C, the gas injection unit 41 having the structure shown in FIG. 14 wasused, and the inner resonator was used instead of the inner coil 542.The high frequency power was not applied to the outer coil 541.

The test results shown in FIGS. 17A to 17C were obtained mainly underthe following conditions.

-   -   Pressure in the chamber 11: 10 to 400 mT    -   Processing gas: Ar=100 to 1500 sccm    -   High frequency power supplied to the inner resonator: 100 to 650        W    -   Frequency of the high frequency power supplied to the inner        resonator: 60 MHz

As shown in FIGS. 17A to 17C, for example, even when the inner resonatoris provided near the gas injection unit 41, in the gas injection unit 41of the second embodiment which has therein the shielding member 420, theoccurrence of abnormal discharge was considerably suppressed, comparedto the test result (see FIGS. 8A to 8C) obtained in the gas injectionunit 41 having no shielding member 420. By providing the shieldingmember 420 around the space in the gas injection unit 41 where theprocessing gas flows, even when the inner resonator is provided near thegas injection unit 41, the occurrence of abnormal discharge in the gasinjection unit 41 can be suppressed. In addition, by replacing the innercoil 542 with the inner resonator, the occurrence of abnormal dischargein the gas injection unit 41 can be further suppressed.

In the second embodiment, the plate-shaped shielding member 420 (seeFIG. 14) and the rod-shaped shielding members 420 (see FIG. 15) areprovided around the space 430 a. However, the arrangement of theshielding members 420 is not limited. As shown in FIG. 18, for example,the plate-shaped shielding member 420 may be buried in the sidewall ofthe gas injection unit 41 to surround the spaces 430 a and 430 b.Besides, as shown in FIG. 19, for example, the shielding member 420 maybe provided at the outer wall of the gas injection unit 41. For example,after a metal film of the shielding member 420 is formed by thermallyspraying a metal forming the shielding member 420 on the sidewall of thegas injection unit 41, ceramic or the like may be further sprayed on thesurface of the shielding member 420.

Third Embodiment

If the space in the gas injection unit 41 where the processing gas flowsis linearly extended in the Z-axis direction, electrons are likely to beaccelerated in the Z-axis direction and abnormal discharge is likely tooccur in the space in the gas injection unit 41. Therefore, in the thirdembodiment, the space in the gas injection unit 41 is formed such that alength of the space extended linearly in the Z-axis direction becomesshort.

FIG. 20 shows an example of the structure of the gas injection unit 41in the third embodiment. Among the components shown in FIG. 20, thecomponents denoted by like reference numerals as those of the componentsshown in FIG. 7 have the same functions as those described withreference to FIG. 7, except for the following features. Therefore,detailed description thereof will be omitted.

As shown in FIG. 20, for example, at least a part of the space 430 awhere the gas injected from the injection ports 43 a flows is bent toprevent formation of a linear path extending from the injection ports 43a to the upper end of the gas injection unit 41. Similarly, at least apart of the space 430 b where the gas injected from the injection ports43 b flows is bent to prevent formation of a linear path extending fromthe injection ports 43 b to the upper end of the gas injection unit 41.The spaces 430 a and 430 b have a so-called labyrinth structure.

FIGS. 21A to 21C show examples of test results obtained by examiningwhether or not discharge has occurred in the third embodiment. FIG. 21Ashows the test result obtained when the pressure in the chamber 11 is 10mT. FIG. 21B shows the test result obtained when the pressure in thechamber 11 is 100 mT. FIG. 21C shows the test result obtained when thepressure in the chamber 11 is 400 mT. In the test shown in FIGS. 21A to21C, the gas injection unit 41 having the structure shown in FIG. 20 wasused, and the inner resonator was used instead of the inner coil 542.The high frequency power was not applied to the outer coil 541.

The test results shown in FIGS. 21A to 21C were obtained mainly underthe following conditions.

-   -   Pressure in the chamber 11: 10 to 400 mT    -   Processing gas: Ar=100 to 1500 sccm    -   High frequency power supplied to the inner resonator: 100 to 650        W    -   Frequency of the high frequency power supplied to the inner        resonator: 60 MHz

As shown in FIGS. 21A to 21C, for example, even when the inner resonatoris provided near the gas injection unit 41, in the gas injection unit 41of the present embodiment in which the space in the gas injection unit41 has a labyrinth structure, the occurrence of abnormal discharge wasconsiderably suppressed, compared to the test result (see FIGS. 8A to8C) obtained in the gas injection unit 41 (see FIG. 7) in which thespace in the gas injection unit 41 does not have a labyrinth structure.By allowing the space in the gas injection unit 41 where the processinggas flows to have a labyrinth structure, even when the inner resonatoris provided near the gas injection unit 41, the occurrence of abnormaldischarge in the gas injection unit 41 can be suppressed. In addition,by replacing the inner coil 542 with the inner resonator, the occurrenceof abnormal discharge in the gas injection unit 41 can be furthersuppressed.

The spaces 430 a and 430 b in the gas injection unit 41 where theprocessing gas flows may be formed such that a spiral-shaped gas flowpath can be formed from the injection ports 43 a and 43 b to the upperend of the gas injection unit 41 as can be seen from FIG. 22, forexample.

(Other Applications)

The present disclosure is not limited to the above-describedembodiments, and various modifications can be made within the scope ofthe gist of the present disclosure.

In the above-described embodiments, the processing gas is supplied intothe chamber 11 from the gas injection unit provided substantially at thecentral portion of the dielectric window 53. However, a plurality ofinjection ports for injecting the processing gas toward the Z-axis maybe provided in the circumferential direction along the sidewall of thechamber 11, in addition to the gas injection unit 41.

In each of the second and third embodiment, each of the injection ports43 b may be configured to inject the processing gas in a direction awayfrom the Z-axis, i.e., in an obliquely downward direction, as shown inFIG. 13, for example.

While the present disclosure has been shown and described with respectto the embodiments, it will be understood by those skilled in the artthat various changes and modifications may be made without departingfrom the scope of the present disclosure as defined in the followingclaims.

What is claimed is:
 1. A plasma processing apparatus comprising: achamber configured to accommodate a target substrate; a dielectricwindow forming an upper portion of the chamber; a gas supply unitconfigured to supply a processing gas from an upper portion of thechamber into the chamber; an antenna provided above the chamber tosurround the gas supply unit and configured to generate plasma of theprocessing gas in the chamber by supplying a high frequency power intothe chamber; and a power supply unit configured to supply a highfrequency power to the antenna, wherein the antenna includes: an innercoil provided around the gas supply unit to surround the gas supplyunit; and an outer coil provided around the gas supply unit and theinner coil to surround the gas supply unit and the inner coil, whereinone of the inner coil and the outer coil is configured such that bothends of a wire forming said one coil are opened; power is supplied fromthe power supply unit to a central point of the wire or a vicinity ofthe central point of the wire; the vicinity of the central point of thewire is grounded; and said one coil resonates at a wavelength that is ahalf of a wavelength of the high frequency power supplied from the powersupply unit, and the other one of the inner coil and the outer coil isconfigured such that both ends of a wire forming the other coil areconnected through a capacitor and the other coil is inductively coupledwith said one coil.
 2. The plasma processing apparatus of claim 1,wherein said one coil is wound two or more turns in a substantiallycircular spiral shape, the other coil is formed in a substantiallycircular ring shape, and said one coil and the other coil are arrangedsuch that an outer shape of said one coil and an outer shape of theother coil form concentric circles.
 3. The plasma processing apparatusof claim 2, wherein the gas supply unit has a substantially cylindricalshape, and said one coil and the other coil are arranged such that acenter of the outer shape of said one coil and a center of the outershape of the other coil are positioned on a central axis of the gassupply unit.
 4. The plasma processing apparatus of claim 1, wherein saidone coil and the other coil are arranged inside the dielectric window orabove the dielectric window, and a distance between a plane includingsaid one coil and a lower surface of the dielectric window is differentfrom a distance between a plane including the other coil and the lowersurface of the dielectric window.
 5. The plasma processing apparatus ofclaim 4, wherein said one coil is the outer coil, the other coil is theinner coil, and the distance between the plane including the inner coiland the lower surface of the dielectric window is shorter than thedistance between the plane including the outer coil and the lowersurface of the dielectric window.
 6. The plasma processing apparatus ofclaim 1, wherein the power supply unit allows a frequency of the highfrequency power supplied to the antenna to be variable.
 7. The plasmaprocessing apparatus of claim 1, wherein the capacitor provided at theother coil is a variable capacitance capacitor.
 8. The plasma processingapparatus of claim 1, wherein a flow path through which the processinggas supplied to the chamber flows is formed in the gas supply unit, anda pressure in the flow path is higher than a pressure in the chamber. 9.The plasma processing apparatus of claim 1, wherein the gas supply unitincludes: a protruding part that is a lower part of the gas supply unitand protrudes into the chamber from the lower surface of the dielectricwindow; a first injection port provided at the protruding part andconfigured to inject the processing gas in a downward direction, and asecond injection port provided at the protruding part and configured toinject the processing gas in a horizontal direction or in an obliquelydownward direction.
 10. The plasma processing apparatus of claim 9,wherein a conductive shielding member is provided at the gas supply unitto surround a space through which the processing gas passes.
 11. Theplasma processing apparatus of claim 10, wherein a lower end of theshielding member is positioned below the lower surface of the dielectricwindow.
 12. The plasma processing apparatus of claim 10, wherein theshielding member is formed in a plate shape.
 13. The plasma processingapparatus of claim 10, wherein the shielding member is a metal filmformed on an outer wall of the gas supply unit or a sidewall of a spacein the gas supply unit through which the processing gas flows.
 14. Theplasma processing apparatus of claim 10, wherein the shielding member isformed in a rod shape.
 15. The plasma processing apparatus of claim 9,wherein at least a part of the space in the gas supply unit throughwhich the processing gas flows is bent to prevent formation of a linearpath extending from the first injection port and the second injectionport to an upper end of the gas supply unit.
 16. A plasma processingapparatus comprising: a chamber configured to accommodate a targetsubstrate; a dielectric window forming an upper portion of the chamber;a gas supply unit configured to supply a processing gas into the chamberfrom an upper portion of the chamber; an antenna provided above thechamber to surround the gas supply unit and configured to generateplasma of the processing gas in the chamber by supplying a highfrequency power into the chamber; and a power supply unit configured tosupply a high frequency power to the antenna, wherein the antenna isprovided around the gas supply unit to surround the gas supply unit;both ends of a wire forming the antenna are opened; power is suppliedfrom the power supply unit to a central point of the wire or to avicinity of the central point of the wire; the vicinity of the centralpoint of the wire is grounded; and the antenna is configured to resonateat a wavelength that is a half of a wavelength of the high frequencypower supplied from the power supply unit, and a conductive shieldingmember is provided at the gas supply unit to surround a space throughwhich the processing gas flows.
 17. The plasma processing apparatus ofclaim 16, wherein a lower end of the shielding member is positionedbelow a lower surface of the dielectric window.
 18. The plasmaprocessing apparatus of claim 16, wherein the shielding member is formedin a plate shape.
 19. The plasma processing apparatus of claim 16,wherein the shielding member is a metal film formed on an outer wall ofthe gas supply unit or a sidewall of a space in the gas supply unitthrough which the processing gas flows.
 20. The plasma processingapparatus of claim 16, wherein the shielding member is formed in a rodshape.
 21. The plasma processing apparatus of claim 16, wherein the gassupply unit includes: a protruding part that is a lower part of the gassupply unit and protrudes into the chamber from the lower surface of thedielectric window; a first injection port provided at the protrudingpart and configured to inject the processing gas in a downwarddirection; and a second injection port provided at the protruding partand configured to inject the processing gas in a horizontal direction orin an obliquely downward direction, wherein at least a part of the spacein the gas supply unit through which the processing gas flows is bent toprevent formation of a linear path extending from the first injectionport and the second injection port to the upper end of the gas supplyunit.